Stabilized polyphenylene sulfide fiber

ABSTRACT

The heat stability of arylene sulfide resins, such as poly(p-phenylene sulfide) resin, is improved by the addition of cure retarders comprising Group IIA or Group IIB metal salts of fatty acids. The resin compositions of the invention are particularly applicable for reducing gel formation during melt extrusion.

FIELD OF INVENTION

This invention relates to improving the characteristics of arylenesulfide polymer compositions. In accordance with another aspect, thisinvention relates to the use of cure retarders in poly(arylene sulfide)resin compositions. In accordance with another aspect, this inventionrelates to the use of cure retarders and heat stabilizers inpoly(arylene sulfide) resin compositions to prevent cross-linking orsubstantial alteration of physical properties during heating. Inaccordance with a further aspect, this invention relates to the use ofselected stabilizers to improve the heat stability of arylene sulfidepolymer compositions, especially poly(p-phenylene sulfide) resins. Inaccordance with a further aspect, this invention relates to improvingthe heat stability of fiber and film grade poly(p-phenylene sulfide)resins by the addition of a cure retarder or stabilizer. In accordancewith still another aspect, this invention relates to the use ofstabilizers that reduce gel formation of arylene sulfide resins whensubjected to heating while processing, for example, during the meltspinning of arylene sulfide resin compositions to produce fibers.

BACKGROUND OF THE INVENTION

In applications, such as in the production of fibers and films fromarylene sulfide polymers, it is desirable that the melt flow andmolecular weight of the polymer remain substantially unchanged duringprocessing of the polymer. Various procedures have been utilized tostabilize arylene sulfide polymers against changes in physicalproperties during processing. It has now been discovered that arylenesulfide polymers can be treated in a manner such that the polymerproperties remain substantially unchanged during heating of the polymerby incorporating into the polymer a cure retarder.

Accordingly, an object of this invention is to provide a process forimproving the heat stability of arylene sulfide polymers.

A further object of this invention is to provide an improved process forstabilizing the physical properties, especially melt flow and molecularweight, of arylene sulfide resins during processing.

A further object of this invention is to provide arylene sulfidepolymers having improved physical properties with respect to melt flowand molecular weight, in particular.

A further object of this invention is to provide phenylene sulfidepolymers exhibiting improved heat stability.

Other objects, aspects, and the several advantages of the invention willbe apparent to those skilled in the art upon a study of thespecification and the appended claims.

SUMMARY OF THE INVENTION

According to the invention, the heat stability of arylene sulfide resinsis improved by the addition of an effective stabilizing amount of atleast one Group IIA or Group IIB metal salt of a fatty acid whichretards curing and cross-linking of the resin during heating.

In accordance with another embodiment of the invention, the heatstability of poly(arylene sulfide) resins, for example, poly(p-phenylenesulfide) resins, is improved by incorporating therein prior to heatingto processing conditions an effective stabilizing amount of at least oneGroup IIA or Group IIB metal salt of a fatty acid to retard curing andcross-linking during heating and processing of the polymer.

In accordance with still another embodiment of the invention, the heatstability of film or fiber grade poly(p-phenylene sulfide) polymers isimproved by the addition of Group IIA or Group IIB metal salts of fattyacids.

In accordance with a further specific embodiment of the invention, theaddition of Group IIA or Group IIB metal salts of fatty acids to arylenesulfide polymer resin compositions reduces the amount of gel formedduring melt extrusion of the polymer composition, thereby minimizingplugging of filters and spinnerets which ordinarily causes prematureshut-downs and additional clean-up operations.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention is applicable for use with any normally solid, heatcurable, high molecular weight arylene sulfide polymer that can beformed into fiber and film. Arylene sulfide polymers which can beemployed in the process of this invention include arylene sulfidepolymers which have a melt flow of at least about 20 and generallywithin the range of about 50 to about 400 and higher (determined by themethod of ASTM D 1238-70, modified to a temperature of 316° C. using a5-kg weight, the value being expressed as g/10 min.). Thus, the arylenesulfide polymers can be linear, branched or lightly cross-linked.Although the method by which the polymers of this description areproduced is not critical, preferably the polymer employed in the processis prepared by use of polyhalo aromatic ompounds, alkali metal sulfides,and organic amides. The preferred type polymer employed for use in fiberand film applications is prepared by use of a p-dihalobenzene, an alkalimetal sulfide, an organic amide, and an alkali metal carboxylate as inU.S. Pat. No. 3,919,177. The disclosure of U.S. Pat. No. 3,919,177 ishereby incorporated by reference.

The Group IIA or Group IIB metal salts of fatty acids useful as cureretarders and heat stabilizers according to the invention, can berepresented by the following structure

    [CH.sub.3 (CH.sub.2).sub.n COO--.sub.2 M

where M is a Group IIA or Group IIB metal and n is an integer from 8 to18.

Representative compounds of the type described above include calciumstearate, calcium laurate, calcium caprate, calcium palmitate, calciumarachidate, zinc stearate, zinc laurate, cadmium stearate, cadmiumlaurate, magnesium stearate, magnesium palmitate, barium stearate,strontium stearate, and the like, and mixtures thereof.

The amount of cure retarder incorporated into the arylene sulfide resinwill be a finite, effective amount sufficient to improve the heatstability of the polymer. In general, the cure retardant additives ofthis invention are employed in an amount within the range of about 0.1to about 5, preferably about 0.5 to 2 weight percent based on the weightof the arylene sulfide polymer.

In addition to the cure retardant additives of this invention, thecompositions can contain other ingredients conventionally employed inarylene sulfide polymer compositions formed into fibers and films. Forinstance, fillers such as zinc oxide, pigments, resins, and/orplasticizers, and the like can be present so long as the particle sizeis small enough to permit passage of polymer through the processingequipment during formation of fibers and films.

The cure retarder can be incorporated into the arylene sulfide polymerat any stage of processing, preferably prior to being subjected toelevated temperature, or at such times as it is desired to retain meltflow stability. In one practical application of the invention, the cureretarders are incorporated into the arylene sulfide resin, such as apoly(p-phenylene sulfide) resin, prior to melt spinning to form fibersor other formed articles so that gel formation is reduced during meltspinning and problems with filter and spinneret plugging is reduced orobviated.

The processes of this invention of incorporating the cure retarder intothe resin can be conducted batch-wise or continuously.

The following examples are intended to illustrate the compositions andprocess of the invention.

EXAMPLE I

This example describes the procedure used to prepare and test samplesdisclosed herein. The example is also a control giving the results ofpoly(p-phenylene sulfide) polymer without an additive. About 10 grams ofpoly(p-phenylene sulfide) power (Mw about 28,000, melt flow 324 gramsper 10 mins. using 5-kg wt. at 316° C. produced by the method describedin U.S. Pat. No. 3,919,177) was treated with about 40 millilitersacetone solvent and dried at ambient room temperature for about 48hours. The dried powder was compression molded into disc specimens, 2.5grams each being 1 inch in diameter x 0.1875 inches thick. The moldingprocedure was 10,000 psig for 5 seconds at about 24° C., 10,000 psig for2.5 minutes at 325° C., 30,000 psig for 2.5 minutes at 325° C., andcooling under pressure to below about 120° C. before removal. The moldeddisc specimens were evaluated by determining storage modulus as afunction of time. Storage modulus is very sensitive to cross-linking andincreases in molecular weight and as such is useful in determining heatstability of polyphenylene sulfide. The test is carried out on aRheometric Dynamic Spectrometer (RDS) available from Rheometrics, Inc.,which comprises two 1 inch diameter stainless steel plates, the bottomplate connected to a sensing device and the top plate able to oscillatehorizontally. The sample to be tested is placed between the plates whichhave been preheated to 300° C. (572° F.). As the sample begins to melt,it is squeezed to a thickness of 2 mm. Excess materials is removed andthe sample allowed to thermally equilibrate for 3 minutes. The top plateis then oscillated at 10 radians per second with 10 percent strain.Readings are recorded every minute for 20 minutes. In this manner theRDS storage modulus after 6 minutes was determined as 1890 dynes persquare centimeter. After 20 minutes RDS storage modulus was 4960 dynesper square centimeter. Thus, the percent difference in storage modulusbetween 6 and 20 minutes was 162 percent.

EXAMPLE II

This is a control run demonstrating the ineffectiveness of some knownstabilizers to retard curing when used in polyphenylene sulfidepolymers. The procedure for sample preparation and evaluation describedin Example I was repeated except that 0.1 gram ofbis(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)dithiol terephthalate(Cyanamid 1729) dissolved in 40 milliliters of acetone was added to thepolyphenylene sulfide powder before the initial drying. The additive andpolyphenylene sulfide powder mixture was periodically stirred during a48 hour ambient run temperature drying period. The procedure wasrepeated with another additive solution, namely, 0.1 gram ofN,N'-diphenyl-p-phenylenediamine (Naugard J) dissolved in 40 millilitersof acetone. The testing results indicate neither of the known stabilizeradditives was effective in reducing gel formation (cross-linking orincreased molecular weight) as determined by RDS storage modulus. Theterephthalate additive had a storage modulus of 2030 dynes/cm² at 6minutes, 5710 dynes/cm² at 20 minutes with a 181 percent change. Theamine stabilizer additive had a storage modulus of 2050 dynes/cm² at 6minutes, 5400 dynes/cm² at 20 minutes with a 163 percent change.

EXAMPLE III

This example is an inventive run demonstrating the effectiveness ofGroup IIA and IIB metal stearates in retarding the cure ofpoly(p-phenylene sulfide) polymers. The procedure for sample preparationand evaluation described in Example I was repeated except that 0.1 gram(1 weight percent) of zinc stearate dissolved in 40 milliliters oftoluene was added to the poly(p-phenylene sulfide) powder before theinitial drying. The additive and the poly(p-phenylene sulfide) powdermixture was periodically stirred during a 48 hour ambient runtemperature drying period. The procedure was repeated with toluenesolutions of magnesium stearate and calcium stearate. The effect ofthese additives on RDS storage modulus is listed in Table I along withthe controls from Examples I and II for comparison. The data indicatesthat not all known stabilizers are effective in retarding cure ofpoly(p-phenylene sulfide) polymer, see controls, Example II. However,the metal stearates of the instant invention are effective in retardingcure of the poly(p-phenylene sulfide) polymer, the most effective beingthe calcium and zinc salts.

                  TABLE I                                                         ______________________________________                                        Effect of Group IIA or Group IIB Metal Stearates                              on Heat Stability (Storage Modulus) of Poly(p-phenylene) Sulfide                                   RDS Storage                                                                   Modulus, dynes/cm.sup.2                                  Example                    6      20   % Dif-                                 No.     1 wt. % Additive   min.   mins.                                                                              ference                                ______________________________________                                        Controls:                                                                     I       No additive        1890   4960 162                                    II      Bis(4-t-butyl-3-hydroxy-2,6-                                                                     2030   5710 181                                            dimethylbenzyl)dithiol                                                        terephthalate.sup.a                                                   II      N,N'--Diphenyl-p-phenylene-                                                                      2050   5400 163                                            diamine.sup.b                                                         Invention:                                                                    III     Magnesium Stearate 2680   5950 122                                    III     Calcium Stearate   2460   4900  99                                    III     Zinc Stearate      1740   3375  94                                    ______________________________________                                         .sup.a Cyanamid 1729 from American Cyanamid, white powder, mp                 218-220° C.                                                            .sup.b Naugard J from Uniroyal                                           

We claim:
 1. In a process for melt extruding fiber grade poly(arylenesulfide) resin having a melt flow of about 50 to about 400 into a fiber,the improvement for reducing gel formation during melt extrusion of saidresin into a fiber which comprises incorporating into siad resin aneffective heat and melt flow stabilizing amount of at least one GroupIIA or Group IIB metal salt of a fatty acid which amount is sufficientto retard curing and cross-linking or substantial alteration of physicalproperties during heating of said resin during melt extrusion andthereby minimizing plugging of filters and spinnerets with gel.
 2. Aprocess according to claim 1 wherein said resin is a poly(p-phenylsulfide) resin.
 3. A process according to claim 1 wherein the amount ofstabilizer added ranges from about 0.5 to about 2 weight percent basedon the weight of the arylene sulfide polymer.
 4. A process according toclaim 1 wherein said resin is a poly(p-phenylene sulfide) resin and saidstabilizer is calcium stearate, magnesium stearate or zinc stearate. 5.A process according to claim 4 wherein the amount of stabilizer presentranges from about 0.1 to about 5 weight percent based on the weight ofpoly(arylene sulfide) resin.
 6. A fiber formed according to the processof claim 1.